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* doc/autoconf.texi (Caching Results): Bigger warning about the

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extremely frequent action-in-commands bug.
Move the documentation of AC_CACHE_SAVE and AC_CACHE_LOAD...
(Cache Files): in here.
This commit is contained in:
Akim Demaille 2000-06-13 09:31:55 +00:00
parent 7b3c994a37
commit 0921af6416
3 changed files with 95 additions and 30 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2000-06-13 Akim Demaille <akim@epita.fr>
* doc/autoconf.texi (Caching Results): Bigger warning about the
extremely frequent action-in-commands bug.
Move the documentation of AC_CACHE_SAVE and AC_CACHE_LOAD...
(Cache Files): in here.
2000-06-09 Steven G. Johnson <stevenj@alum.mit.edu>
* acgeneral.m4 (AC_CHECK_TOOL): Even if VALUE-IF-NOT-FOUND is not

6
configure vendored
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@ -1318,6 +1318,12 @@ SHELL=${CONFIG_SHELL-/bin/sh}
config_files="\
acversion.m4 Makefile m4/Makefile man/Makefile doc/Makefile tests/Makefile
tests/atconfig"
EOF
# Be careful that the expansion of AC_LIST_LINKS (which may contain
# uses of shell variables) is itself expanded in an unquoted `here'-document.
cat >>$CONFIG_STATUS <<EOF
EOF
cat >>$CONFIG_STATUS <<\EOF
ac_cs_usage="\
\`$me' instantiates files from templates according to the

112
doc/autoconf.texi
View File

@ -5367,42 +5367,72 @@ Ensure that the results of the check identified by @var{cache-id} are
available. If the results of the check were in the cache file that was
read, and @code{configure} was not given the @option{--quiet} or
@option{--silent} option, print a message saying that the result was
cached; otherwise, run the shell commands @var{commands-to-set-it}.
Those commands should have no side effects except for setting the
variable @var{cache-id}. In particular, they should not call
@code{AC_DEFINE}; the code that follows the call to @code{AC_CACHE_VAL}
should do that, based on the cached value. Also, they should not print
any messages, for example with @code{AC_MSG_CHECKING}; do that before
calling @code{AC_CACHE_VAL}, so the messages are printed regardless of
whether the results of the check are retrieved from the cache or
determined by running the shell commands. If the shell commands are run
to determine the value, the value will be saved in the cache file just
before @code{configure} creates its output files. @xref{Cache
Variable Names}, for how to choose the name of the @var{cache-id} variable.
cached; otherwise, run the shell commands @var{commands-to-set-it}. If
the shell commands are run to determine the value, the value will be
saved in the cache file just before @code{configure} creates its output
files. @xref{Cache Variable Names}, for how to choose the name of the
@var{cache-id} variable.
The @var{commands-to-set-it} @emph{must have no side effects} except for
setting the variable @var{cache-id}, see below.
@end defmac
@defmac AC_CACHE_CHECK (@var{message}, @var{cache-id}, @var{commands})
@defmac AC_CACHE_CHECK (@var{message}, @var{cache-id}, @var{commands-to-set-it})
@maindex CACHE_CHECK
A wrapper for @code{AC_CACHE_VAL} that takes care of printing the
messages. This macro provides a convenient shorthand for the most
common way to use these macros. It calls @code{AC_MSG_CHECKING} for
@var{message}, then @code{AC_CACHE_VAL} with the @var{cache-id} and
@var{commands} arguments, and @code{AC_MSG_RESULT} with @var{cache-id}.
The @var{commands-to-set-it} @emph{must have no side effects} except for
setting the variable @var{cache-id}, see below.
@end defmac
@defmac AC_CACHE_LOAD
@maindex CACHE_LOAD
Loads values from existing cache file, or creates a new cache file if a
cache file is not found. Called automatically from @code{AC_INIT}.
@end defmac
It is very common to find buggy macros using @code{AC_CACHE_VAL} or
@code{AC_CACHE_CHECK} because people are tempted to call
@code{AC_DEFINE} in the @var{commands-to-set-it}. It is the code that
follows the call to @code{AC_CACHE_VAL} should do that, based on the
cached value. For instance the following macro:
@defmac AC_CACHE_SAVE
@maindex CACHE_SAVE
Flushes all cached values to the cache file. Called automatically from
@code{AC_OUTPUT}, but it can be quite useful to call
@code{AC_CACHE_SAVE} at key points in configure.in. Doing so
checkpoints the cache in case of an early configure script abort.
@end defmac
@example
@group
AC_DEFUN([AC_SHELL_TRUE],
[AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works],
[ac_cv_shell_true_works=no
true && ac_cv_shell_true_works=yes
if test $ac_cv_shell_true_works = yes; then
AC_DEFINE([TRUE_WORKS], 1
[Define if `true(1)' works properly.])
fi[]dnl
])])
@end group
@end example
@noindent
is broken: if the cache is enabled, the second time this macro is run,
@code{TRUE_WORKS} @emph{will not be defined}. The proper implementation
is:
@example
@group
AC_DEFUN([AC_SHELL_TRUE],
[AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works],
[ac_cv_shell_true_works=no
true && ac_cv_shell_true_works=yes])
if test $ac_cv_shell_true_works = yes; then
AC_DEFINE([TRUE_WORKS], 1
[Define if `true(1)' works properly.])
fi[]dnl
])
@end group
@end example
Also, @var{commands-to-set-it} should not print any messages, for
example with @code{AC_MSG_CHECKING}; do that before calling
@code{AC_CACHE_VAL}, so the messages are printed regardless of whether
the results of the check are retrieved from the cache or determined by
running the shell commands.
@menu
* Cache Variable Names:: Shell variables used in caches
@ -5493,29 +5523,51 @@ site-wide cache file to use instead of the default, to make it work
transparently, as long as the same C compiler is used every time
(@pxref{Site Defaults}).
If your configure script, or a macro called from configure.in, happens to
abort the configure process, it may be useful to checkpoint the cache a
few times at key points. Doing so will reduce the amount of time it
takes to re-run the configure script with (hopefully) the error that
caused the previous abort corrected.
If your configure script, or a macro called from configure.in, happens
to abort the configure process, it may be useful to checkpoint the cache
a few times at key points using @code{AC_CACHE_SAVE}. Doing so will
reduce the amount of time it takes to re-run the configure script with
(hopefully) the error that caused the previous abort corrected.
@c FIXME: Do we really want to document this guy?
@defmac AC_CACHE_LOAD
@maindex CACHE_LOAD
Loads values from existing cache file, or creates a new cache file if a
cache file is not found. Called automatically from @code{AC_INIT}.
@end defmac
@defmac AC_CACHE_SAVE
@maindex CACHE_SAVE
Flushes all cached values to the cache file. Called automatically from
@code{AC_OUTPUT}, but it can be quite useful to call
@code{AC_CACHE_SAVE} at key points in configure.in.
@end defmac
For instance:
@example
@r{ ... AC_INIT, etc. ...}
@group
# Checks for programs.
AC_PROG_CC
AC_PROG_GCC_TRADITIONAL
@r{ ... more program checks ...}
AC_CACHE_SAVE
@end group
@group
# Checks for libraries.
AC_CHECK_LIB(nsl, gethostbyname)
AC_CHECK_LIB(socket, connect)
@r{ ... more lib checks ...}
AC_CACHE_SAVE
@end group
@group
# Might abort...
AM_PATH_GTK(1.0.2,, (exit 1); exit)
AM_PATH_GTKMM(0.9.5,, (exit 1); exit)
@end group
@r{ ... AC_OUTPUT, etc. ...}
@end example